Hi Guys! I've scoured these pages the last couple days, but can't find anything that matches my specific dilemma.
I have a 1990 Wrangler w/ 150k miles on it, recent acquisition by my future son-in-law. It was running relatively fine, but it quit suddenly on a recent trip. It started cutting out when hitting bumps, then finally quit altogether.
After dragging it home, hitting the forums, swapping a few parts, following all the sensor tests and wrapping my head around this TBI setup, I am afraid I have a partially dead ECU.
-All ignition parts replaced- Ignition Module, Coil, Wires, Cap and Rotor, Plugs.
-The truck will crank the engine just fine, but has NO spark at coil or plugs, and NO gas at the injector. The fuel pump comes on with ignition switch for 1-2 sec, there is fuel in the line at the throttle body, I have not checked fuel pressure yet.
-A new CPS was installed, I checked the CPS, 217 Ohms (slightly low), 0.54 VAC while cranking the engine.
- All other sensors checked out nominal. There is 5 VDC to the TPS and MAP sensors, so the ECU is not entirely fried.
-While tracing the sensor wiring, I found a wire broken internally between the CPS sensor and the ECU (red-white wire tied to pin 28), I'm guessing that was the root cause of the failure. I'm afraid the ECU board may have been damaged in the process of the wire failing while driving.
-I am looking for information about what I should be seeing for the output signals for the Ignition Module and Fuel Injector from the ECU. I expect they will be low voltage AC pulses, grounding the DC power supplied to the Ignition Module and the Injector. I have not found any specifications for the AC voltage or pulse duration for either the Ignition at pin 27 or Injector at pin 21 of the ECU. I measured both of these signals while cranking the engine, I got ~0.1 VAC at the injector, and basically zero (0.004 VAC) at the ignition module output. These numbers lead me to believe that the output drivers for these functions are damaged or dead, although I can see no signs of physical damage, no burnt smell, melted traces, cracks, or corrosion anywhere in the ecu components.
Is there any function programmed in the ECU which would completely shut down the spark- and injector-outputs based on some combination of other inputs for some safety reason ?
Any info on the specific layout of components relating to the Ignition and Injector Drivers in the 1987-1990 ECU would be greatly appreciated! And Thank You to all who have gone before me here, the info trail has been invaluable!!